The present invention relates to novel parasite protease genes, proteins encoded by such genes, antibodies raised against such proteins, and protease inhibitors produced using such proteins. Particular proteases of the present invention include astacin metalloendopeptidases and cysteine proteases. The present invention also includes therapeutic compositions comprising such nucleic acid molecules, proteins, antibodies and inhibitors, as well as their use to protect animals from disease caused by parasites, such as by tissue-migrating helminths such as heartworm.
Parasite infections in animals, including humans, are typically treated by chemical drugs, because there are essentially no efficacious vaccines available. One disadvantage with chemical drugs is that they must be administered often. For example, dogs susceptible to heartworm are typically treated monthly to maintain protective drug levels. Repeated administration of drugs to treat parasite infections, however, often leads to the development of resistant strains that no longer respond to treatment. Furthermore, many of the chemical drugs are harmful to the animals being treated, and as larger doses become required due to the build up of resistance, the side effects become even greater.
It is particularly difficult to develop vaccines against parasite infections both because of the complexity of the parasite""s life cycle and because, while administration of parasites or parasite antigens can lead to the production of a significant antibody response, the immune response is typically not sufficient to protect the animal against infection.
As for most parasites, the life cycle of Dirofilaria immitis, the helminth that causes heartworm, includes a variety of life forms, each of which presents different targets, and challenges, for immunization. Adult forms of the parasite are quite large and preferentially inhabit the heart and pulmonary arteries of an animal. Males worms are typically about 12 centimeters (cm) to about 20 cm long and about 0.7 millimeters (mm) to about 0.9 mm wide; female worms are about 25 cm to about 31 cm long and about 1.0 to about 1.3 mm wide. Sexually mature adults, after mating, produce microfilariae which are only about 300 micrometers (xcexcm) long and about 7 xcexcm wide. The microfilariae traverse capillary beds and circulate in the vascular system of dogs in concentrations of about 103 to about 105 microfilariae per milliliter (ml) of blood. One method of demonstrating infection in dogs is to detect the circulating microfilariae.
If dogs are maintained in an insect-free environment, the life cycle of the parasite cannot progress. However, when microfilariae are ingested by female mosquitos during blood feeding on an infected dog, subsequent development of the microfilariae into larvae occurs in the mosquito. The microfilariae go through two larval stages (L1 and L2) and finally become mature third stage larvae (L3) of about 1.1 mm length, which can then be transmitted back to a dog through the bite of the mosquito. It is this L3 stage, therefore, that accounts for the initial infection. As early as three days after infection, the L3 molt to the fourth larval (L4) stage, and subsequently to the fifth stage, or immature adults. The immature adults migrate to the heart and pulmonary arteries, where they mature and reproduce, thus producing the microfilariae in the blood. xe2x80x9cOccultxe2x80x9d infection with heartworm in dogs is defined as an infection in which no microfilariae can be detected, but the existence of adult heartworms can be determined through thoracic examination.
Both the molting process and tissue migration are likely to involve the action of one or more enzymes, including proteases. Although protease activity has been identified in a number of parasites (including in larval excretory-secretory products) as well as in mammals, there apparently has been no identification of an astacin metalloendopeptidase gene in any parasite or of a cysteine protease gene in any filariid.
Astacin metalloendopeptidases, so-called because of their similarity to the metalloendopeptidase astacin found in crayfish, are a relatively newly recognized class of metalloproteases that have been found in humans, mice and rats as well as apparently in Drosophila fruit flies, Xenopus frogs and sea urchins; see, for example, Gomis-Ruth et al., 1993, J. Mol. Biol. 229, 945-968; Jiang et al., 1992, FEBS Letters 312, 110-114; and Dumermuth et al., 1991, J. Biol. Chem. 266, 21381-21385. Human intestinal and mouse kidney brush border metalloendopeptidases share about 82 percent homology in the amino-terminal 198 amino acids. Both share about 30 percent homology with astacin and with the amino-terminal domain of human bone morphogenetic protein 1. Members of the astacin family share an extended zinc-binding domain motif, the consensus sequence of which was identified by Dumermuth et al., ibid., as being HEXXHXXGFXHE, denoted SEQ ID NO:37, wherein H is histidine, E is glutamic acid, G is glycine, F is phenylalanine and X can be any amino acid. Gomis-Ruth et al., ibid., define the zinc-binding domain motif as His-Glu-Uaa-Xaa-His-Xaa-Uaa-Gly-Uaa-Xaa-His, denoted SEQ ID NO:38, wherein Uaa is a bulky apolar residue-containing amino acid. Jiang et al., ibid., disclose not only the extended zinc-binding domain motif, which they represent as HEIGHAIGFXHE, denoted SEQ ID NO:39, (italicized letters being strictly conserved) but also two other sequences conserved between astacin metalloendopeptidases, including RXDRD, denoted SEQ ID NO:40, spanning amino acids from about 15 through about 19 and YDYXSIMHY, denoted SEQ ID NO:41, spanning amino acids from about 50 through about 58, assuming that the first histidine in the extended zinc-binding domain motif is amino acid position 1. The three histidines at positions 1, 5 and 11 appear to be responsible for zinc binding as is the tyrosine at position 58. The glutamic acid at position 2 is responsible for catalysis. Other key amino acids include the glycine at position 8 which is involved in secondary structure and the glutamic acid at position 12 which forms a salt bridge with the amino-terminus of the mature enzyme.
Consensus sequences, particularly around the active sites, have also been identified for serine and cysteine proteases; see, for example, Sakanari et al., 1989, Proc. Natl. Acad. Sci. USA 86, 4863-4867. Although cysteine protease genes have been isolated from several mammalian sources and from the nematodes Haemonchus contortus (e.g., Pratt et al., 1992, Mol. Biochem. Parasitol. 51, 209-218) and Caenorhabditis elegans (Ray et al., 1992, Mol. Biochem. Parasitol. 51, 239-250), the cloning of such genes does not necessarily predict that the cloning of novel cysteine protease genes will be straight-forward, particularly since the sequences shared by different cysteine proteases are such that probes and primers based on the consensus sequences are highly degenerative.
Heartworm not only is a major problem in dogs, which typically are unable to develop immunity after infection (i.e., dogs can become reinfected even after being cured by chemotherapy), but is also becoming increasingly widespread in other companion animals, such as cats and ferrets. Heartworm infections have also been reported in humans. Other parasite infections are also widespread, and all require better treatment, including preventative vaccine programs and/or targeted drug therapies.
One embodiment of the present invention is an isolated parasite nucleic acid molecule capable of hybridizing, under stringent conditions, with a Dirofilaria immitis astacin metalloendopeptidase gene. Such a nucleic acid molecule, namely a parasite astacin metalloendopeptidase nucleic acid molecule, can include a regulatory region of a parasite astacin metalloendopeptidase gene and/or encode at least a portion of a parasite astacin metalloendopeptidase protein.
A preferred nucleic acid molecule of the present invention includes at least a portion of SEQ ID NO:1, of SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO: 30, SEQ ID NO:32 and/or SEQ ID NO:33, or the complement thereof. The present invention also includes recombinant molecules and recombinant cells that include parasite astacin metalloendopeptidase nucleic acid molecules of the present invention. Also included are methods to produce such nucleic acids, recombinant molecules and recombinant cells of the present invention.
Another embodiment of the present invention is an isolated protein that includes a parasite astacin metalloendopeptidase protein or a mimetope of such a protein. A parasite astacin metalloendopeptidase protein of the present invention preferably has astacin metalloendopeptidase activity and/or comprises a protein that, when administered to an animal in an effective manner, is capable of eliciting an immune response against a natural parasite astacin metalloendopeptidase protein. The present invention also includes inhibitors of astacin metalloendopeptidase activity as well as antibodies that recognize (i.e., selectively bind to) a parasite astacin metalloendopeptidase protein and/or mimetope thereof of the present invention. Also included are methods to produce such proteins, inhibitors and antibodies of the present invention.
Yet another embodiment of the present invention is an isolated filariid nematode nucleic acid molecule capable of hybridizing, under stringent conditions, with a D. immitis cysteine protease gene. Such a nucleic acid molecule, namely a filariid cysteine protease nucleic acid molecule, can include a regulatory region of a filariid cysteine protease gene and/or encode at least a portion of a filariid cysteine protease protein. A preferred nucleic acid molecule of the present invention includes at least a portion of SEQ ID NO:12. The present invention also includes recombinant molecules and recombinant cells that include filariid cysteine protease nucleic acid molecules of the present invention. Also included are methods to produce such nucleic acids, recombinant molecules and recombinant cells of the present invention.
Another embodiment of the present invention is an isolated protein that includes a filariid cysteine protease protein or a mimetope of such a protein. A filariid cysteine protease protein of the present invention preferably has cysteine protease activity and/or comprises a protein that, when administered to an animal in an effective manner, is capable of eliciting an immune response against a natural filariid cysteine protease protein. The present invention also includes inhibitors of cysteine protease activity as well as antibodies that recognize (i.e., selectively bind to) a filariid cysteine protease protein and/or mimetope thereof of the present invention. Also included are methods to produce such proteins, inhibitors and antibodies of the present invention.
Yet another embodiment of the present invention is a therapeutic composition capable of protecting an animal from disease caused by a parasite. Such a therapeutic composition includes at least one of the following protective compounds: an isolated parasite astacin metalloendopeptidase protein or a mimetope thereof; an isolated parasite nucleic acid molecule capable of hybridizing under stringent conditions with a D. immitis astacin metalloendopeptidase gene; an anti-parasite astacin metalloendopeptidase antibody; an inhibitor of astacin metalloendopeptidase activity identified by its ability to inhibit parasite astacin metalloendopeptidase activity; an isolated filariid nematode cysteine protease protein or a mimetope thereof; an isolated filariid nematode nucleic acid molecule capable of hybridizing under stringent conditions with a D. immitis cysteine protease gene; an anti-filariid nematode cysteine protease antibody; and an inhibitor of cysteine protease activity identified by its ability to inhibit filariid nematode cysteine protease activity. Also included is a method to protect an animal from disease caused by a parasite that includes administering to the animal in an effective manner a therapeutic composition of the present invention. A preferred therapeutic composition of the present invention is a composition capable of protecting an animal from heartworm.
The present invention also includes a method to identify a compound capable of inhibiting astacin metalloendopeptidase activity of a parasite. Such a method includes (a) contacting an isolated parasite astacin metalloendopeptidase protein with a putative inhibitory compound under conditions in which, in the absence of the compound, the astacin metalloendopeptidase protein has astacin metalloendopeptidase activity; and (b) determining if the putative inhibitory compound inhibits astacin metalloendopeptidase activity. Also included is a test kit to identify a compound capable of inhibiting astacin metalloendopeptidase activity that includes an isolated parasite astacin metalloendopeptidase protein having astacin metalloendopeptidase activity and a means for determining the extent of inhibition of astacin metalloendopeptidase activity in the presence of a putative inhibitory compound.
Also included in the present invention is a method to identify a compound capable of inhibiting cysteine protease activity of a parasite. Such a method includes (a) contacting an isolated filariid cysteine protease protein with a putative inhibitory compound under conditions in which, in the absence of the compound, the filariid cysteine protease protein has cysteine protease activity; and (b) determining if the putative inhibitory compound inhibits cysteine protease activity. Also included is a test kit to identify a compound capable of inhibiting cysteine protease activity of a parasite that includes an isolated filariid cysteine protease protein having cysteine protease activity and a means for determining the extent of inhibition of cysteine protease activity in the presence of a putative inhibitory compound.
The present invention includes the discovery that parasites such as D. immitis express astacin metalloendopeptidases. As such, the present invention includes nucleic acid molecules encoding such proteins as well as the proteins themselves. To the inventors"" knowledge, astacin metalloendopeptidases have been found previously only in humans, mice, rats, crayfish, Drosophila, Xenopus, sea urchins, chorioallontoic membranes of quail eggs, and medaka fish (Oryzias latipes). The present invention also includes the first identification and isolation of nucleic acid molecules encoding filariid nematode cysteine proteases as well as the cysteine proteases themselves, after a difficult and time-consuming search by the inventors for such nucleic acid molecules. Isolated nucleic acid molecules and proteins of the present invention, including homologues of such nucleic acid molecules and proteins, are useful both in protecting animals from parasite infections and in other applications, including those disclosed below.
One embodiment of the present invention is an isolated parasite (or parasitic) astacin metalloendopeptidase protein or a mimetope thereof (i.e., a mimetope of a parasite astacin metalloendopeptidase protein). According to the present invention, an isolated, or biologically pure, protein, is a protein that has been removed from its natural milieu. As such, xe2x80x9cisolatedxe2x80x9d and xe2x80x9cbiologically purexe2x80x9d do not necessarily reflect the extent to which the protein has been purified. An isolated parasite astacin metalloendopeptidase protein can be obtained from its natural source. Such an isolated protein can also be produced using recombinant DNA technology or chemical synthesis.
As used herein, an isolated parasite astacin metalloendopeptidase protein can be a full-length protein or any homologue of such a protein, such as a protein in which amino acids have been deleted (e.g., a truncated version of the protein, such as a peptide), inserted, inverted, substituted and/or derivatized (e.g., by glycosylation, phosphorylation, acetylation, myristylation, prenylation, palmitation, amidation and/or addition of glycosylphosphatidyl inositol) such that the homologue has astacin metalloendopeptidase activity and/or is capable of eliciting an immune response against a natural D. immitis astacin metalloendopeptidase protein. As used herein, an astacin metalloendopeptidase protein, the full-length version of which is a protein that includes an extended zinc-binding domain, has characteristics similar to astacin and other members of the xe2x80x9castacin family of metalloendopeptidasesxe2x80x9d; see, for example, Dumermuth et al., ibid. A protein having astacin metalloendopeptidase activity is a protein that can cleave proteins in a manner similar to the zinc-dependent protease astacin. Astacin activity is inhibited by metal chelators such as ethylene diamine tetraacetic acid (EDTA) and 1,10-phenanthroline but not by phosphoramidon, an inhibitor of several other metalloproteases including thermolysin and neutral endopeptidases. Tissue inhibitors of metalloproteinases (TIMP1 and TIMP2), which are the best characterized protein inhibitors of zinc endopeptidases, do not demonstrate inhibitory activity with astacin (Stocker and Zwillig, 1995, Methods of Enzymology, vol. 248). Astacin activity can be detected by those skilled in the art (see, for example, Dumermuth et al., ibid.). A protein capable of eliciting an immune response against a natural protein is a protein that includes at least one epitope capable of eliciting an immune response (humoral and/or cellular) against that natural protein (such as a D. immitis astacin metalloendopeptidase or a D. immitis cysteine protease) when the protein (e.g., the natural protein or a homologue thereof) is administered to an animal as an immunogen using techniques known to those skilled in the art. The ability of a protein to effect an immune response can be measured using techniques known to those skilled in the art. Examples of methods to measure an immune response (e.g., antibody detection, resistance to infection) are disclosed herein.
A parasite astacin metalloendopeptidase protein of the present invention, including a homologue of the full-length protein, has the further characteristic of being encoded by a nucleic acid molecule that is capable of hybridizing, under stringent conditions, with (i.e., to) a D. immitis astacin metalloendopeptidase gene. A preferred astacin metalloendopeptidase protein of the present invention is encoded by a nucleic acid molecule capable of hybridizing, under stringent conditions, with at least a portion of the complement of the nucleic acid sequence disclosed in SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO: 30, SEQ ID NO:32 and/or SEQ ID NO:33. As used herein, the phrase xe2x80x9cat least a portion ofxe2x80x9d an entity refers to an amount of the entity that is at least sufficient to have the functional aspects of that entity. For example, at least a portion of a nucleic acid sequence, as used herein, is an amount of a nucleic acid sequence capable of forming a stable hybrid under stringent hybridization conditions. As used herein, stringent hybridization conditions refer to standard hybridization conditions under which nucleic acid molecules (or sequences), including oligonucleotides, are used to identify similar sequences. Such standard conditions are disclosed, for example, in Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Labs Press, 1989.
Stringent hybridization conditions typically permit isolation of nucleic acid molecules having at least about 70% nucleic acid sequence identity with the nucleic acid molecule being used as a probe in the hybridization reaction. Formulae to calculate the appropriate hybridization an wash conditions to achieve hybridization permitting 30% or less mis-match between two nucleic acid molecules are disclosed, for example, in Meinkoth et al, 1984, Anal. Biochem 138, 267-284; Meinkoth et al, ibid, is incorporated by reference herein in its entirety. An example of such conditions includes, but is not limited to, the following: Oligonucleotide probes of about 18-25 nucleotides in length with Tm""s ranging from about 50xc2x0 C. to about 65xc2x0 C., for example, can be hybridized to nucleic acid molecules typically immobilized on a filter (e.g., nitrocellulose filter) in a solution containing 2xc3x97 SSPE, 1% Sarkosyl, 5xc3x97 Denhardts and 0.1 mg/ml denatured salmon sperm DNA at a temperature as calculated using the formulae of Meinkoth et al., ibid. for about 2 to about 12 hours. The filters are then washed 3 times in a wash solution containing 2xc3x97 SSPE, 1% Sarkosyl at about 55xc2x0 C. for about 15 minutes each. The filters can be further washed in a wash solution containing 2xc3x97 SSPE, 1% Sarkosyl at about 55xc2x0 C. for about 15 minutes per wash. Further examples of such conditions are provided in the Examples section.
It should be noted that the extent of homology required to form a stable hybrid can vary depending on whether the homologous sequences are interspersed throughout the nucleic acid molecules or are clustered (i.e., localized) in distinct regions on the nucleic acid molecules. Also in accordance with present invention, at least a portion of a astacin metalloendopeptidase protein is a protein of sufficient size to have astacin metalloendopeptidase activity and/or to be able to elicit an immune response against a natural parasite astacin metalloendopeptidase.
SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:32 and SEQ ID NO:33 represent the nucleotide sequences of six cDNA (complementary DNA) nucleic acid molecules denoted nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, and adult nDiMPA32028, respectively, the production of which is disclosed in the Examples. It should be noted that since nucleic acid sequencing technology is not entirely error-free, SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:32 and SEQ ID NO:33 represent, at best, apparent nucleic acid sequences of the respective nucleic acid molecules. As will be discussed in greater detail below, nucleic acid molecules nDiMPA11299 and nDiMPA22126 apparently comprise overlapping open reading frames, as deduced from SEQ ID NO:1 and SEQ ID NO:2. Each of the nucleic acid molecules L3 nDiMPA32292 and adult nDiMPA32032 apparently comprises a single open reading frame as deduced from SEQ ID NO:29 and SEQ ID NO:32, denoted L3 nDiMPA32076 (SEQ ID NO:30) and adult nDiMPA32028 (SEQ ID NO:33), respectively. The deduced amino acid sequences encoded by L3 nDiMPA32076 and adult nDiMPA32028 are disclosed, respectively, in SEQ ID NO:31 and SEQ ID NO:34. Nucleic acid molecule nDiMPA11299 apparently comprises three open reading frames, referred to herein as PDiMPA1ORF1, PDiMPA1ORF2 and PDiMPA1ORF3, the deduced amino acid sequences of which are disclosed, respectively, in SEQ ID NO:3, SEQ ID NO:4 and SEQ ID NO:5. Nucleic acid molecule nDiMPA22126 apparently comprises five open reading frames, referred to herein as PDiMPA2ORF1, PDiMPA2ORF2, PDiMPA2ORF3, PDiMPA2ORF4 and PDiMPA2ORF5, the deduced amino acid sequences of which are disclosed, respectively, in SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9 and SEQ ID NO:10. That the open reading frames on both nucleic acid molecules are overlapping raises the possibility that translation of a functional astacin metalloendopeptidase in vivo may involve frameshifting. Both SEQ ID NO:1 and SEQ ID NO:2 contain nucleic acid sequences, including stem-loop structures, that, for frameshift viral gene expression, have been implicated in ribosome slowing and, hence, frameshift translation. The presence of stem loop structures in the mRNA could have caused the reverse transcriptase to stutter or misread the mRNA during the Dirofilaria cDNA library construction. This lack of faithful reproduction of the cDNA from the mRNA template could account for the base pairs missing in the original cDNA clones obtained from the library having the nucleic acid sequences SEQ ID NO:1 and SEQ ID NO:2. Alternatively, nucleic acid molecules nDiMPA11299 and nDiMPA22126 may also be the result of alternative splicing patterns.
L3 nDiMPA32292 apparently comprises a single open reading frame, referred to herein as L3 nDiMPA32076 (SEQ ID NO:30), which encodes a protein, namely PDiMPA3692, the deduced amino acid sequence of which is disclosed in SEQ ID NO:31. Adult nDiMPA32032 also apparently comprises a single open reading frame, referred to herein as adult nDiMPA32028 (SEQ ID NO:33), which encodes a protein, namely adult PDiMPA3676, the deduced amino acid sequence of which is disclosed in SEQ ID NO:34.
SEQ ID NO:11 represents a composite amino acid sequence derived from the five open reading frames encoded by nDiMPA22126. As such, SEQ ID NO:11 is an example of a combination of disclosed open reading frames, in this case a combination of PDiMPA2ORF1, PDiMPA2ORF2, PDiMPA2ORF3, PdiMPA2ORF4 and PDiMPA2ORF5. The astacin domain of SEQ ID NO:11 has about 29 percent amino acid sequence homology (i.e., identity within comparable regions) with the amino acid sequence of crayfish astacin. As used herein, an astacin domain is an amino acid sequence of about 200 amino acids that shares significant homology with crayfish astacin, which is a 202-amino acid protein. The astacin domain of SEQ ID NO:11 spans from about amino acid positions 98 through 299. The astacin domain of SEQ ID NO:11 also shares about 30 percent, 31 percent, 33 percent and 33 percent homology at the amino acid level with the astacin domains of, respectively, human bone morphogenetic protein 1, mouse kidney brush border metalloendopeptidase, human intestinal brush border metalloendopeptidases and Xenopus laevis embryonic protein UVS.2 (using sequences provided in Dumermuth et al., ibid.).
SEQ ID NO:31 represents the deduced amino acid sequence of the single open reading frame of L3 nDiMPA32292, which is represented herein as nucleic acid molecule L3 nDiMPA32076 (SEQ ID NO:30). The astacin domain of SEQ ID NO:31 spans amino acid positions from about 122 through 326. The astacin domain of SEQ ID NO:31 shares about 27.3 percent, 31.7 percent, and 34.1 percent homology at the amino acid level with the astacin domains of, respectively, crayfish astacin, quail astacin and the C. elegans R151.5 gene product, (Genbank accession number U00036). SEQ ID NO:31 shows about 81.7% homology with the composite amino acid sequence derived from the five open reading frames encoded by nDiMPA22126 (SEQ ID NO:11).
SEQ ID NO:34 represents the deduced amino acid sequence of the single open reading frame of adult nDiMPA320321 which is represented herein as nucleic acid molecule adult nDiMPA32028 (SEQ ID NO:33). The astacin domain of SEQ ID NO:34 spans from about amino acid positions 122 through 326. The astacin domain of SEQ ID NO:34 shares about 26.3 percent, 31.2 percent, and 34.6 percent homology at the amino acid level with the astacin domains of, respectively, crayfish astacin, quail astacin and the C. elegans R151.5 gene product, (Genbank accession number U00036). SEQ ID NO:34 shows about 81.3% homology with the composite amino acid sequence derived from the five open reading frames encoded by nDiMPA22126 (SEQ ID NO:11).
The amino acid sequences presented as SEQ ID NO:31 (L3 PDiMPA3692) and SEQ ID NO:34 (adult PDiMPA3676) contain three regions of homology which are conserved within about a 61 amino acid region of all known astacins. In L3 PDiMPA3692 and adult PDiMPA3676, these three regions span about a 60 amino acid sequence corresponding to amino acid positions from about 214 through about 273 of L3 PDiMPA3692, and to amino acid positions from about 198 through about 257 of adult PDiMPA3676 (as numbered in SEQ ID NO:31 and SEQ ID NO:34, respectively). The first region of homology includes the zinc binding domain, which spans positions from about 214 through about 224 of SEQ ID NO:31 and positions from about 198 through about 208 of SEQ ID NO:34. This first region includes three histidines which are present in all astacins for zinc binding (imidazole zinc ligands) at positions 214, 218 and 224 of SEQ ID NO:31 and at positions 198, 202 and 208 of SEQ ID NO:34, and a glutamate at position 215 of SEQ ID NO:31 and at position 199 of SEQ ID NO:34, which is assumed to be catalytically important in all astacins. In addition, this first region includes a glycine which is important for secondary structure of the protein at position 221 of SEQ ID NO:31 and at position 205 of SEQ ID NO:34, and a glutamate which forms a salt bridge with the amino terminus of the mature astacin protein at position 225 of SEQ ID NO:31 and at position 209 of SEQ ID NO:34.
The second region found in L3 PDiMPA3692 and adult PDiMPA3676 that is conserved in all known astacins spans amino acid positions 228 through 232 of SEQ ID NO:31 and positions 212 through 216 of SEQ ID NO:34. This second region is a hydrophilic region common to all astacins.
The third region found in L3 PDiMPA3692 and adult PDiMPA3676 that is conserved in all known astacins spans amino acid positions 265 through 273 of SEQ ID NO:31 and positions 249 through 257 of SEQ ID NO:34, and contains a portion of the zinc binding domain. In particular, the hydroxyl oxygen of the tyrosine at position 273 of SEQ ID NO:31 and position 257 of SEQ ID NO:34 is the fourth amino acid zinc ligand. It has been proposed that the catalytically active zinc ion of astacins is penta-coordinated with a water molecule serving as the fifth zinc ligand (Stocker et al., 1993, Eur. J. Biochem.) In many known astacins, this tyrosine is typically at position 61 from the first amino acid of the zinc binding domain (i.e., 61 amino acids from the first histidine in the first region). In L3 PDiMPA3692 and adult PDiMPA3676, this tyrosine is at position 60 from the first amino acid of the zinc binding domain (i.e., 60 amino acids from the first histidine in the first region at position 214 of SEQ ID NO:31 and position 198 of SEQ ID NO:34).
A preferred astacin metalloendopeptidase protein of the present invention includes an amino acid sequence having at least about 35 percent, more preferably at least about 45 percent, even more preferably at least about 60 percent and even more preferably at least about 75 percent, amino acid homology with the astacin domain of SEQ ID NO:11 (i.e., with the corresponding regions of the astacin domain of SEQ ID NO:11). A more preferred astacin metalloendopeptidase protein of the present invention includes an amino acid sequence having at least about 40 percent, more preferably at least about 45 percent, even more preferably at least about 60 percent and even more preferably at least about 75 percent, amino acid homology with the astacin domain of SEQ ID NO:31 or SEQ ID NO:34. An even more preferred astacin metalloendopeptidase protein of the present invention includes at least a portion of at least one of the following open reading frames: PDiMPA1ORF1, PDiMPA1ORF2, PDiMPA1ORF3, PDiMPA2ORF1, PDiMPA2ORF2, PDiMPA2ORF3, PDiMPA2ORF4, PDiMPA2ORF5, L3 PDiMPA3692 and adult PDiMPA3676, the deduced amino acid sequences of which are disclosed, respectively, in SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:31 and SEQ ID NO:34. Preferred astacin metalloendopeptidase proteins of the present invention include an extended zinc-binding domain motif. More preferred astacin metalloendopeptidase proteins also contain the tyrosine zinc binding amino acid-containing domain as identified by Jiang et al., ibid, and disclosed above.
Parasite astacin metalloendopeptidase protein homologues can be the result of natural allelic variation or natural mutation. Homologues can also be produced using techniques known in the art including, but not limited to, direct modifications to the protein or modifications to the gene encoding the protein using, for example, classic or recombinant DNA techniques to effect random or targeted mutagenesis. Isolated astacin metalloendopeptidase proteins of the present invention, including homologues, can be identified in a straight-forward manner by the proteins"" ability to effect astacin metalloendopeptidase activity and/or to elicit an immune response against parasite astacin metalloendopeptidase proteins. Examples of such identification techniques are disclosed herein.
The minimum size of an isolated protein of the present invention is sufficient to form an epitope, a size that is typically at least from about 7 to about 9 amino acids. As is appreciated by those skilled in the art, an epitope can include amino acids that naturally are contiguous to each other as well as amino acids that, due to the tertiary structure of the natural protein, are in sufficiently close proximity to form an epitope.
Any parasite astacin metalloendopeptidase is a suitable protein of the present invention. Suitable parasites from which to isolate proteins (including isolation of the natural protein or production of the protein by recombinant or synthetic techniques) include parasitic helminths, protozoa and ectoparasites such as, but not limited to nematodes, cestodes, trematodes, fleas, flies, ticks, lice, true bugs, and protozoa of the genera Babesia, Cryptosporidium, Eimeria, Encephalitozoon, Hepatozoon, Isospora, Leishmania, Neospora, Nosema, Plasmodium, Pneumocystis, Theileria, Toxoplasma and Trypanosoma. Preferred parasites include tissue-migrating parasitic helminths, and particularly tissue-migrating nematodes. Preferred nematodes include filariid, ascarid, strongyle and trichostrongyle nematodes. Particularly preferred tissue-migrating nematodes include parasites of the genera Acanthocheilonema, Aelurostrongylus, Ancylostoma, Angiostrongylus, Ascaris, Brugia, Bunostomum, Dictyocaulus,
Dioctophyme, Dipetalonema, Dirofilaria, Dracunculus, Filaroides, Lagochilascaris, Loa, Mansonella, Muellerius, Necator, Onchocerca, Parafilaria, Parascaris, Protostrongylus, Setaria, Stephanofilaria, Strongyloides, Strongylus, Thelazia, Toxascaris, Toxocara, Trichinella, Uncinaria and Wuchereria. Other particularly preferred nematodes include parasites of the genera Capillaria, Chabertia, Cooperia, Enterobius, Haemonchus, Nematodirus, Oesophagostomum, Ostertagia, Trichostrongylus and Trichuris. Preferred filariid nematodes include Dirofilaria, Acanthocheilonema, Brugia, Dipetalonema, Loa, Onchocerca, Parafilaria, Setaria, Stephanofilaria and Wuchereria filariid nematodes. A particularly preferred parasite is a nematode of the genus Dirofilaria, with D. immitis, the parasite that causes heartworm, being even more preferred.
In accordance with the present invention, a mimetope of a protein refers to any compound that is able to mimic the activity of that protein, often because the mimetope has a structure that mimics the protein. For example, a mimetope of a parasite astacin metalloendopeptidase protein is a compound that has an activity similar to that of an isolated parasite astacin metalloendopeptidase protein of the present invention. Mimetopes can be, but are not limited to: peptides that have been modified to decrease their susceptibility to degradation; anti-idiotypic and/or catalytic antibodies, or fragments thereof; non-proteinaceous immunogenic portions of an isolated protein (e.g., carbohydrate structures); and synthetic or natural organic molecules, including nucleic acids. Such mimetopes can be designed using computer-generated structures of proteins of the present invention. Mimetopes can also be obtained by generating random samples of molecules, such as oligonucleotides, peptides or other organic molecules, and screening such samples by affinity chromatography techniques using, for example, antibodies raised against a protein of the present invention.
A preferred parasite astacin metalloendopeptidase protein or mimetope of the present invention is a compound that when administered to an animal in an effective manner, is capable of protecting that animal from disease caused by a parasite that is susceptible to treatment to inhibit astacin metalloendopeptidase activity. As such, the parasite preferably is essentially incapable of causing disease in an animal that is immunized with a parasite astacin metalloendopeptidase protein, and preferably with a D. immitis astacin metalloendopeptidase protein, of the present invention. In accordance with the present invention, the ability of a protein or mimetope of the present invention to protect an animal from disease by a parasite refers to the ability of that protein or mimetope to treat, ameliorate and/or prevent disease, including infection leading to disease, caused by the parasite, preferably by eliciting an immune response against the parasite. Such an immune response can include humoral and/or cellular immune responses. Suitable parasites to target include any parasite that is essentially incapable of causing disease in an animal administered a parasite astacin metalloendopeptidase protein of the present invention. As such, a parasite to target includes any parasite that produces a protein having one or more epitopes that can be targeted by a humoral and/or cellular response against a parasite astacin metalloendopeptidase protein of the present invention and/or that can be targeted by a compound that is capable of substantially inhibiting parasite astacin metalloendopeptidase activity, thereby resulting in the reduced ability of the parasite to cause disease in an animal. Suitable and preferred parasites to target include those parasites disclosed above. A preferred class of parasites to target include tissue-migrating parasitic helminths. A particularly preferred nematode helminth to target is D. immitis, which causes heartworm.
One embodiment of the present invention is a fusion protein that includes a parasite astacin metalloendopeptidase domain attached to a fusion segment. Inclusion of a fusion segment as part of a protein of the present invention can enhance the protein""s stability during production, storage and/or use. Depending on the segment""s characteristics, a fusion segment can also act as an immunopotentiator to enhance the immune response mounted by an animal immunized with a protein of the present invention that contains such a fusion segment. Furthermore, a fusion segment can function as tool to simplify purification of a protein of the present invention, such as to enable purification of the resultant fusion protein using affinity chromatography. A suitable fusion segment can be a domain of any size that has the desired function (e.g., imparts increased stability to a protein, imparts increased immunogenicity to a protein, and/or simplifies purification of a protein). It is within the scope of the present invention to use one or more fusion segments. Fusion segments can be joined to amino and/or carboxyl termini of the astacin metalloendopeptidase-containing domain of the protein. Linkages between fusion segments and astacin metalloendopeptidase-containing domains of fusion proteins can be susceptible to cleavage in order to enable straight-forward recovery of the astacin metalloendopeptidase-containing domains of such proteins. Fusion proteins are preferably produced by culturing a recombinant cell transformed with a fusion nucleic acid molecule that encodes a protein including the fusion segment attached to either the carboxyl and/or amino terminal end of an parasite astacin metalloendopeptidase-containing domain.
Preferred fusion segments for use in the present invention include a glutathione binding domain, such as Schistosoma japonicum glutathione-S-transferase (GST) or a portion thereof capable of binding to glutathione; a metal binding domain, such as a poly-histidine segment capable of binding to a divalent metal ion; an immunoglobulin binding domain, such as Protein A, Protein G, T cell, B cell, Fc receptor or complement protein antibody-binding domains; a sugar binding domain such as a maltose binding domain from a maltose binding protein; and/or a xe2x80x9ctagxe2x80x9d domain (e.g., at least a portion of xcex2-galactosidase, a strep tag peptide, other domains that can be purified using compounds that bind to the domain, such as monoclonal antibodies). More preferred fusion segments include metal binding domains, such as a poly-histidine segment; a maltose binding domain; a strep tag peptide, such as that available from Biometra in Tampa, Fla.; and an S10 peptide. An example of a preferred fusion protein of the present invention is PHIS-PDiMPA2804, the production of which is disclosed herein.
Another embodiment of the present invention is a parasite astacin metalloendopeptidase protein that also includes at least one additional protein segment that is capable of protecting an animal from one or more diseases. Such a multivalent protective protein can be produced by culturing a cell transformed with a nucleic acid molecule comprising two or more nucleic acid domains joined together in such a manner that the resulting nucleic acid molecule is expressed as a multivalent protective compound containing at least two protective compounds, or portions thereof, capable of protecting an animal from diseases caused, for example, by at least one infectious agent.
Examples of multivalent protective compounds include, but are not limited to, a parasite astacin metalloendopeptidase protein attached to one or more other parasite proteins, such to a filariid nematode cysteine protease protein of the present invention. Other examples of multivalent protective compounds include a parasite astacin metalloendopeptidase protein attached to one or more compounds protective against one or more other infectious agents, particularly an agent that infects cats or dogs, such as, but not limited to, calicivirus, distemper virus, feline herpesvirus, feline immunodeficiency virus, feline leukemia virus, feline infectious peritonitis, hepatitis, hookworm, leptospirosis, panleukopenia virus, parvovirus, rabies and toxoplasmosis.
Suitable heartworm multivalent protective proteins include, but are not limited to, a D. immitis astacin metalloendopeptidase and/or a D. immitis cysteine protease of the present invention attached to at least one other D. immitis protein such as, but not limited to, a D. immitis Gp29 protein, a D. immitis P 39 protein, a D. immitis P22U protein, a D. immitis P22L protein, a D. immitis P20.5 protein, a D. immitis P4 protein, a D. immitis Di22 protein and/or a D. immitis protease expressed in L3 and/or L4 larvae, as well as other helminth proteins sharing significant homology with such D. immitis proteins. A protein sharing significant homology with another protein refers to the ability of the nucleic acid sequences encoding such proteins to form stable hybridization complexes with each other under stringent hybridization conditions, as described, for example, in Sambrook et al., ibid. U.S. patent application Ser. No. 08/208,885, now U.S. Pat. No. 5,567,603 filed Mar. 8, 1994, entitled xe2x80x9cD. immitis Gp29 Proteins, Nucleic Acid Molecules and Uses Thereofxe2x80x9d, discloses D. immitis Gp29 proteins and nucleic acid molecules that encode them. U.S. patent application Ser. No. 08/003,389, now abandoned, filed Jan. 12, 1993, entitled xe2x80x9cImmunogenic Larval Proteinsxe2x80x9d, discloses a 39-kD (kilodalton) D. immitis protein (size determined by Tris glycine SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis)), referred to herein as P39, and a nucleic acid sequence that encodes it. U.S. patent application Ser. No. 08/003,257, now abandoned, filed Jan. 12, 1993, entitled xe2x80x9cReagents and Methods for Identification of Vaccinesxe2x80x9d, discloses 22-kD and 20.5-kD D. immitis proteins (sizes determined by Tris glycine SDS-PAGE), referred to herein as P22L and P20.5, and nucleic acid sequences that encode them. U.S. patent application Ser. No. 08/109,391, now U.S. Pat. No. 5,639,876, filed Aug. 19, 1993, entitled xe2x80x9cNovel Parasitic Helminth Proteinsxe2x80x9d, discloses D. immitis P4 and D. immitis P22U, as well as nucleic acid sequences that encode them. U.S. patent application Ser. No. 08/060,500, now abandoned filed May 10, 1993, entitled xe2x80x9cHeartworm Vaccinexe2x80x9d, discloses a D. immitis Di22 protein and a nucleic acid sequence encoding it (included in Genbank data base accession number M82811); Ser. No. 08/060,500 is a continuation of U.S. patent application Ser. No. 07/683,202, now abandoned, filed Apr. 8, 1991. U.S. patent application Ser. No. 08/153,554, now abandoned, filed Nov. 16, 1993, entitled xe2x80x9cProtease Vaccine Against Heartwormxe2x80x9d, discloses D. immitis larval proteases; Ser. No. 08/153,554 now abandoned, is a continuation of U.S. patent application Ser. No. 07/792,209, now abandoned, filed Nov. 12, 1991. Each of these patent applications is incorporated by reference herein in its entirety.
A particularly preferred parasite astacin metalloendopeptidase protein is a protein encoded by at least a portion of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:32 and SEQ ID NO:33, and, as such, is a protein having an amino acid sequence encoded by at least a portion of at least one of the open reading frames encoding an amino acid sequence represented by SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:31 and/or SEQ ID NO:34. Preferred proteins can include combinations of amino acid sequences encoded by such reading frames, such as SEQ ID NO:11, that result in a functional protein. A homology search using these open reading frames indicate that all but SEQ ID NO:10 share significant homology with known members of the astacin metalloendopeptidase family and with a Caenorhabditis elegans R151.5 gene product, Genbank accession number U00036 (Wilson et al., 1994, Nature 368, 32-38), suggesting that C. elegans also encodes a astacin metalloendopeptidase. Particularly well conserved are the extended zinc-binding domain motif and the tyrosine-containing domain motif, the overall sequence homology being about 24 percent. Even more preferred proteins are encoded by single reading frames which encode a protein having an amino acid sequence of SEQ ID NO:31 or SEQ ID NO:34. A homology search using these open reading frames indicate that they also share significant homology with known members of the astacin metalloendopeptidase family and with a Caenorhabditis elegans R151.5 gene product, Genbank accession number U00036 (Wilson et al., supra). Again, particularly well conserved are the extended zinc-binding domain motif and the tyrosine-containing domain motif, the overall sequence homology being about 34.5 percent.
Particularly preferred proteins of the present invention include proteins having the astacin domain of SEQ ID NO:11, proteins having the astacin domain of SEQ ID NO:31, proteins having the astacin domain of SEQ ID NO:34, proteins that include these domains (such as, but not limited to, full-length proteins, fusion proteins and proteins providing multivalent protection) and proteins that are truncated homologues of these domains. Even more preferred proteins include PDiMPA2804, PHIS-PDiMPA2804, L3 PDiMPA3692, and adult PDiMPA3676.
Another embodiment of the present invention is an isolated parasite nucleic acid molecule capable of hybridizing, under stringent conditions, with a D. immitis astacin metalloendopeptidase gene. As used herein, a D. immitis astacin metalloendopeptidase gene includes all nucleic acid sequences related to a natural D. immitis astacin metalloendopeptidase gene such as regulatory regions that control production of a D. immitis astacin metalloendopeptidase protein encoded by that gene (such as, but not limited to, transcription, translation or post-translation control regions) as well as the coding region itself A parasite astacin metalloendopeptidase nucleic acid molecule of the present invention can include any isolated natural parasite astacin metalloendopeptidase gene or a homologue thereof. A nucleic acid molecule of the present invention can include one or more regulatory regions, full-length or partial coding regions, or combinations thereof. The minimal size of a parasite astacin metalloendopeptidase nucleic acid molecule of the present invention is the minimal size capable of forming a stable hybrid under stringent hybridization conditions. Suitable and preferred parasites are disclosed above.
In accordance with the present invention, an isolated nucleic acid molecule is a nucleic acid molecule that has been removed from its natural milieu (i.e., that has been subject to human manipulation). As such, xe2x80x9cisolatedxe2x80x9d does not reflect the extent to which the nucleic acid molecule has been purified. An isolated nucleic acid molecule can include DNA, RNA, or derivatives of either DNA or RNA.
An isolated parasite astacin metalloendopeptidase nucleic acid molecule of the present invention can be obtained from its natural source either as an entire (i.e., complete) gene or a portion thereof capable of forming a stable hybrid with that gene. An isolated parasite astacin metalloendopeptidase nucleic acid molecule can also be produced using recombinant DNA technology (e.g., polymerase chain reaction (PCR) amplification, cloning) or chemical synthesis. Isolated parasite astacin metalloendopeptidase nucleic acid molecules include natural nucleic acid molecules and homologues thereof, including, but not limited to, natural allelic variants and modified nucleic acid molecules in which nucleotides have been inserted, deleted, substituted, and/or inverted in such a manner that such modifications do not substantially interfere with the nucleic acid molecule""s ability to encode a parasite astacin metalloendopeptidase protein of the present invention or to form stable hybrids under stringent conditions with natural isolates.
A parasite astacin metalloendopeptidase nucleic acid molecule homologue can be produced using a number of methods known to those skilled in the art (see, for example, Sambrook et al., ibid.). For example, nucleic acid molecules can be modified using a variety of techniques including, but not limited to, classic mutagenesis techniques and recombinant DNA techniques, such as site-directed mutagenesis, chemical treatment of a nucleic acid molecule to induce mutations, restriction enzyme cleavage of a nucleic acid fragment, ligation of nucleic acid fragments, polymerase chain reaction (PCR) amplification and/or mutagenesis of selected regions of a nucleic acid sequence, synthesis of oligonucleotide mixtures and ligation of mixture groups to xe2x80x9cbuildxe2x80x9d a mixture of nucleic acid molecules and combinations thereof. Nucleic acid molecule homologues can be selected from a mixture of modified nucleic acids by screening for the function of the protein encoded by the nucleic acid (e.g., astacin metalloendopeptidase activity or ability to elicit an immune response against at least one epitope of a parasite astacin metalloendopeptidase protein) and/or by hybridization with isolated parasite astacin metalloendopeptidase nucleic acids under stringent conditions.
An isolated nucleic acid molecule of the present invention can include a nucleic acid sequence that encodes at least one parasite astacin metalloendopeptidase protein of the present invention, examples of such proteins being disclosed herein. Although the phrase xe2x80x9cnucleic acid moleculexe2x80x9d primarily refers to the physical nucleic acid molecule and the phrase xe2x80x9cnucleic acid sequencexe2x80x9d primarily refers to the sequence of nucleotides on the nucleic acid molecule, the two phrases can be used interchangeably, especially with respect to a nucleic acid molecule, or a nucleic acid sequence, being capable of encoding a protein. As heretofore disclosed, parasite astacin metalloendopeptidase proteins of the present invention include, but are not limited to, proteins having full-length astacin metalloendopeptidase coding regions, proteins having partial astacin metalloendopeptidase coding regions, fusion proteins, multivalent protective proteins and combinations thereof.
One embodiment of the present invention is a parasite astacin metalloendopeptidase nucleic acid molecule that is capable of hybridizing under stringent conditions with nucleic acid molecule nDiMPA11299, with nucleic acid molecule nDiMPA22126, with nucleic acid molecule L3 nDiMPA32292, with nucleic acid molecule L3 nDiMPA32076, with nucleic acid molecule adult nDiMPA32032, and/or with nucleic acid molecule adult nDiMPA32028. As such, preferred astacin metalloendopeptidase nucleic acid molecules are capable of forming stable hybrids with nucleic acid molecules represented by SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:32 and/or SEQ ID NO:33. Particularly preferred astacin metalloendopeptidase nucleic acid molecules comprise at least a portion of nucleic acid molecule nDiMPA11299, nucleic acid molecule nDiMPA22126, nucleic acid molecule L3 nDiMPA32292, nucleic acid molecule L3 nDiMPA32076, adult nDiMPA32032, and/or adult nDiMPA32028. As such, a preferred nucleic acid molecule of the present invention includes a nucleic acid sequence including at least a portion of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:32 and/or SEQ ID NO:33. Such a nucleic acid molecule can be nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, and/or adult nDiMPA32028, can include nucleotides in addition to nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, and/or adult nDiMPA32028, or can be a truncation fragment of nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, and/or adult nDiMPA32028. Particularly preferred nucleic acid molecules include nDiMPA1689, nDiMPA11299, nDiMPA22126, nDiMPA2804, nDiMPA2271, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, adult nDiMPA32028, and BvMPA2, the production of which are disclosed in the Examples.
One preferred embodiment of the present invention is a parasite astacin metalloendopeptidase nucleic acid molecule capable of hybridizing to the complement of the coding strand of a nucleic acid molecule encoding at least one open reading frame encoding at least one of the following amino acid sequences: SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:31 and SEQ ID NO:34. Preferably, such a nucleic acid molecule encodes a protein that shares at least about 35 percent, more preferably at least about 45 percent, even more preferably at least about 60 percent and even more preferably at least about 75 percent amino acid homology with SEQ ID NO:11. Even more preferably, such a nucleic acid molecule encodes a protein that shares at least about 40 percent, more preferably at least about 45 percent, even more preferably at least about 60 percent and even more preferably at least about 75 percent amino acid homology with SEQ ID NO:31 and/or SEQ ID NO:34. More preferred astacin metalloendopeptidase nucleic acid molecules encode at least a portion of at least one of such open reading frames. Particularly preferred astacin metalloendopeptidase nucleic acid molecules are capable of forming stable hybrids with nucleic acid molecules encoding an extended zinc-binding domain motif (i.e., to the carboxyl terminus of the motif as well as to the general zinc-binding domain) and, more preferably, also with nucleic acid molecules encoding other disclosed conserved domains of astacin metalloendopeptidases, such as the motif that contains the tyrosine believed to bind to zinc.
Knowing the nucleic acid sequence of certain parasite astacin metalloendopeptidase nucleic acid molecules of the present invention allows one skilled in the art to make copies of those nucleic acid molecules as well as to obtain nucleic acid molecules including at least a portion of such nucleic acid molecules and other parasite astacin metalloendopeptidase nucleic acid molecule homologues. Such nucleic acid molecules can be obtained in a variety of ways including screening appropriate expression libraries with antibodies of the present invention; traditional cloning techniques using oligonucleotide probes of the present invention to screen appropriate libraries or DNA; and PCR amplification of appropriate libraries or DNA using oligonucleotide primers of the present invention. Preferred libraries to screen or from which to amplify include parasite larval (especially L3, L4) and adult cDNA libraries as well as genomic DNA libraries. Similarly, preferred DNA sources to screen or from which to amplify include parasite larval (especially L3, L4) and adult cDNA and genomic DNA. Techniques to clone and amplify genes are disclosed, for example, in Sambrook et al., ibid.
The present invention also includes nucleic acid molecules that are oligonucleotides capable of hybridizing, under stringent conditions, with complementary regions of other, preferably longer, nucleic acid molecules of the present invention, such as to complementary regions of a parasite astacin metalloendopeptidase gene, including complementary regions of a D. immitis astacin metalloendopeptidase gene. Such oligonucleotides can hybridize under stringent conditions with complementary regions of nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, or adult nDiMPA32028, complementary regions of nucleic acid molecules that include at least a portion of nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA320321 or adult nDiMPA32028, and complementary regions of nucleic acid molecules that hybridize under stringent conditions with nDiMPA11299, nDiMPA22126, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, or adult nDiMPA32028. Such oligonucleotides can be RNA, DNA, or derivatives of either. The minimal size of such oligonucleotides is the size required to form a stable hybrid between a given oligonucleotide and the complementary sequence on another nucleic acid molecule of the present invention. As such, the size is dependent on nucleic acid composition and percent homology between the oligonucleotide and complementary sequence as well as upon hybridization conditions per se (e.g., temperature, salt concentration). For AT-rich nucleic acid sequences, such as those of parasitic helminths, oligonucleotides typically are at least about 15 to about 17 bases in length. The size of the oligonucleotide must also be sufficient for the use of the oligonucleotide in accordance with the present invention. Oligonucleotides of the present invention can be used in a variety of applications including, but not limited to, as probes to identify additional nucleic acid molecules, as primers to amplify or extend nucleic acid molecules or in therapeutic applications to inhibit, for example, expression of astacin metalloendopeptidases by a parasite. Such therapeutic applications include the use of such oligonucleotides in, for example, antisense-, triplex formation-, ribozyme- and/or RNA drug-based technologies. The present invention, therefore, includes such oligonucleotides and methods to interfere with the production of astacin metalloendopeptidase proteins by use of one or more of such technologies. Appropriate oligonucleotide-containing therapeutic compositions can be administered to an animal, using techniques known to those skilled in the art, either prior to or after infection by a parasite such as D. immitis, in order to protect the animal from disease.
Another embodiment of the present invention is an isolated filariid nematode cysteine protease protein or a mimetope thereof. As used herein, an isolated filariid nematode, or filariid, cysteine protease protein can be a full-length filariid cysteine protease protein or any homologue of such a protein. Filariid nematode cysteine protease proteins, including homologues thereof, can be isolated and produced according to the methods disclosed herein for parasite astacin metalloendopeptidase proteins. Homologues and mimetopes of filariid cysteine protease proteins are defined in a similar manner as are homologues and mimetopes of parasite astacin metalloendopeptidase proteins. Filariid cysteine protease proteins (including homologues) and mimetopes thereof each are capable of eliciting an immune response (i.e., having at least one epitope capable of eliciting an immune response) against a filariid cysteine protease protein and/or are capable of effecting cysteine protease activity. Cysteine protease activity, as well as the ability of a protein to effect an immune response, can be measured using techniques known to those skilled in the art. Cysteine protease activity can be measured by its ability to cleave peptides having a cysteine protease cleavage site, such as z-Val-Leu-Arg-AMC; such activity can be inhibited by, for example, by the cysteine protease inhibitor E-64 (available from Boehringer Mannheim, Indianapolis, Ind.). Preferred filariids are disclosed herein. A particularly preferred filariid is D. immitis. 
A filariid cysteine protease protein of the present invention, including any homologue thereof, has the additional characteristic of being encoded by a nucleic acid molecule that is capable of hybridizing, under stringent conditions, with the complement of the coding strand of a nucleic acid molecule comprising at least a portion of a nucleic acid sequence encoding a filariid cysteine protease protein. Preferred proteins are encoded by a nucleic acid molecule that forms stable hybrids with at least a portion of nDiCP1431 the production of which is described in detail in the Examples. SEQ ID NO:12 represents the deduced sequence of nDiCP143, the deduced translation product of which is a 47 amino acid sequence represented in SEQ ID NO:13, the protein being denoted PDiCP143. It should be noted that since nucleic acid sequencing technology is not entirely error-free, SEQ ID NO:12, at best, represents an apparent nucleic acid sequence of a nucleic acid molecule encoding at least a portion of full-length D. immitis cysteine protease. Furthermore, SEQ ID NO:13 apparently represents an internal amino acid sequence of D. immitis cysteine protease since SEQ ID NO:12 apparently has neither a start nor stop codon. SEQ ID NO:13, however, includes amino acid sequences that are conserved among a number of cysteine proteases.
A comparison of SEQ ID NO:13 with the corresponding regions of known parasite cysteine protease genes indicates that SEQ ID NO:13 shares about 16 percent, about 22 percent, about 24 percent, about 35 percent, about 39 percent, about 44 percent and about 49 percent homology at the amino acid level with cysteine proteases from, respectively, H. contortus (a nematode), Schistosoma mansoni (a trematode), C. elegans (a nematode), Fasciola hepatica (a trematode), Entamoeba histolytica (a protozoa), Trypanosoma cruzi (a protozoa) and T. brucie. SEQ ID NO:13 also shares about 50 percent amino acid homology with human cathepsin L, about 45 percent amino acid homology with chicken cathepsin L and about 56 percent amino acid homology with a Paragonimus westermani (trematode) cysteine protease. The serine at about position 30 and the cysteine at about position 37 of SEQ ID NO:13 are conserved in all of these cysteine proteases. Please see, for example, the following for listings of the above-referenced sequences: Heussler et al., 1994, Mol. Biochem. Parasitol. 64, 11-23; Eakin et al., 1990, Mol. Biochem. Parasitol. 39, 1-8; Ray et al., ibid., Pratt et al., ibid., Sakanari et al., ibid.; European Patent Application Publication No. 0524834A2, by Hamajima et al., published Jan. 27, 1993.
Preferred filariid cysteine protease proteins of the present invention include amino acid sequences that share at least about 60 percent, more preferably at least about 70 percent, and even more preferably at least about 80 percent, homology with SEQ ID NO:13. Particularly preferred filariid cysteine protease proteins of the present invention include PDiCP142, proteins that include PDiCP142 (including, but not limited to full-length proteins, fusion proteins and multivalent protective proteins), and proteins that include at least a portion of PDiCP142.
A preferred filariid cysteine protease protein or mimetope thereof is a compound that when administered to an animal in an effective manner, is capable of protecting that animal from disease caused by a parasite that is susceptible to treatment with a composition that inhibits cysteine protease activity. A suitable parasite to target is any parasite that produces a protein having one or more epitopes that can be targeted by a humoral and/or cellular response against a filariid nematode cysteine protease protein of the present invention and/or that can be targeted by a compound that is capable of substantially inhibiting filariid cysteine protease activity, thereby resulting in the reduced ability of the parasite to cause disease in an animal. Suitable and preferred parasites are disclosed above. A preferred class of parasites to target include tissue-migrating parasitic helminths. A particularly preferred nematode to target is D. immitis, which causes heartworm.
Also included in the present invention are fusion proteins and multivalent protective proteins that include at least one filariid cysteine protease protein. Such proteins can comprise fusion segments and/or multiple protective domains similar as disclosed for parasite astacin metalloendopeptidase proteins and can be produced in a similar manner as described for parasite astacin metalloendopeptidase proteins of the present invention. Particularly preferred fusion proteins include PHIS-PDiCP142.
Yet another embodiment of the present invention is an isolated filariid nematode nucleic acid molecule capable of hybridizing, under stringent conditions, with a D. immitis cysteine protease gene. Such a nucleic acid molecule is referred to as a filariid nematode, or filariid, cysteine protease nucleic acid molecule. As used herein, a filariid cysteine protease gene includes all nucleic acid sequences related to a natural filariid cysteine protease gene such as regulatory regions that control production of a D. immitis cysteine protease protein encoded by that gene as well as the coding region itself. A filariid cysteine protease nucleic acid molecule of the present invention can include an isolated natural filariid cysteine protease gene or a homologue thereof. A nucleic acid molecule of the present invention can include one or more regulatory regions, full-length or partial coding regions, or combinations thereof. The minimal size of a filariid cysteine protease nucleic acid molecule of the present invention is the minimal size capable of forming a stable hybrid under stringent hybridization conditions with a D. immitis cysteine protease gene. Filariid immitis cysteine protease nucleic acid molecules can be isolated and produced according to the methods taught herein for the production and isolation of parasite astacin metalloendopeptidase nucleic acid molecules. Cysteine protease nucleic acid molecule homologues can be selected from a mixture of modified nucleic acids by screening for the function of the protein encoded by the nucleic acid (e.g., cysteine protease activity and/or ability to elicit an immune response against at least one epitope of a filariid cysteine protease protein) and/or by hybridization with isolated D. immitis cysteine protease nucleic acids under stringent conditions.
An isolated filariid cysteine protease nucleic acid molecule of the present invention can include a nucleic acid sequence that encodes at least one filariid cysteine protease protein of the present invention, examples of such proteins being disclosed herein. As heretofore disclosed, filariid cysteine protease proteins of the present invention include, but are not limited to, proteins having full-length filariid cysteine protease coding regions, proteins having partial filariid cysteine protease coding regions, fusion proteins, multivalent protective proteins and combinations thereof. The present invention also includes nucleic acid molecules encoding filariid cysteine protease proteins that have been modified to accommodate codon usage properties of the cells in which such nucleic acid molecules are to be expressed.
One embodiment of the present invention is a filariid cysteine protease nucleic acid molecule that includes a nucleic acid sequence that is capable of hybridizing under stringent conditions with D. immitis nucleic acid molecule nDiCP143, the deduced sequence of which is disclosed in SEQ ID NO:12. Preferred filariid cysteine protease nucleic acid molecules encode proteins having at least about 60 percent, more preferably at least about 70 percent and even more preferably at least about 80 percent, amino acid homology with SEQ ID NO:13. More preferred is a nucleic acid molecule that encodes a D. immitis cysteine protease protein that comprises at least a portion of SEQ ID NO:13.
A preferred nucleic acid molecule of the present invention includes at least a portion of D. immitis nucleic acid molecule nDiCP143. Such a nucleic acid molecule can be nDiCP143, can include nucleotides in addition to nDiCP143 (such as, but not limited to, a nucleic acid molecule encoding a full-length protein, a nucleic acid molecule encoding a fusion protein, or a nucleic acid molecule encoding a multivalent protective compound), or can be a truncation fragment of nDiCP143. Particularly preferred filariid cysteine protease nucleic acid molecules include nDiCP143 and nDiCP142.
The inventors of the present invention had difficulty isolating a D. immitis cysteine protease nucleic acid molecule despite the wide variety of cysteine protease genes that have been cloned. Primers designed by the inventors using consensus sequences derived from known cysteine protease genes, including from known parasite cysteine protease genes, had a degeneracy that was essentially too great to pull out a D. immitis cysteine protease gene. The inventors discovered that use of primers that incorporated D. immitis codon usage bias enabled the identification of the first D. immitis cysteine protease nucleic acid molecule, namely nDiCP143.
Having identified the nucleic acid molecule nDiCP143, it is likely that one skilled in the art can make copies of that nucleic acid molecule as well as obtain other filariid nematode cysteine protease nucleic acid molecules including full-length genes and homologues thereof. Such nucleic acid molecules can be obtained in a variety of ways such as those described for the isolation and production of parasite astacin metalloendopeptidase nucleic acid molecules of the present invention. Preferred libraries to screen or from which to amplify include filariid larval (especially L3, L4) and adult cDNA libraries and filariid genomic DNA libraries. Similarly, preferred DNA sources to screen or from which to amplify include filariid larval (especially L3, L4) and adult cDNA, as well as filariid genomic DNA. Preferred primers and probes to use are codon-biased for the given filariid.
The present invention also includes nucleic acid molecules that are oligonucleotides capable of hybridizing, under stringent conditions, with complementary regions of other, preferably longer, nucleic acid molecules of the present invention, such as to complementary regions of a filariid cysteine protease gene. Such oligonucleotides can hybridize under stringent conditions with complementary regions of nDiCP143, complementary regions of nucleic acid molecules that include at least a portion of nDiCP143, and complementary regions of nucleic acid molecules that hybridize under stringent conditions with nDiCP143. Such oligonucleotides can be RNA, DNA, or derivatives of either. Other criteria, such as minimal size, as well as methods to produce and use such oligonucleotides are as disclosed for parasite astacin metalloendopeptidase oligonucleotides of the present invention.
The present invention also includes a recombinant vector, which includes at least one nucleic acid molecule of the present invention (e.g., a parasite astacin metalloendopeptidase nucleic acid molecule and/or a filariid cysteine protease nucleic acid molecule, examples of which are disclosed herein) inserted into any vector capable of delivering the nucleic acid molecule into a host cell. Such a vector contains heterologous nucleic acid sequences, that is nucleic acid sequences that are not naturally found adjacent to nucleic acid molecules of the present invention and that preferably are derived from a species other than the species from which the nucleic acid molecule(s) are derived. The vector can be either RNA or DNA, either prokaryotic or eukaryotic, and typically is a virus or a plasmid. Recombinant vectors can be used in the cloning, sequencing, and/or otherwise manipulating of parasite, including D. immitis, nucleic acid molecules of the present invention. One type of recombinant vector, herein referred to as a recombinant molecule and described in more detail below, can be used in the expression of nucleic acid molecules of the present invention. Preferred recombinant vectors are capable of replicating in the transformed cell.
Preferred nucleic acid molecules to include in recombinant vectors of the present invention include at least one of the following: a nucleic acid molecule that includes at least a portion of nDiMPA11299, a nucleic acid molecule that includes at least a portion of nDiMPA22126, a nucleic acid molecule that includes at least a portion of L3 nDiMPA32292, a nucleic acid molecule that includes at least a portion of L3 nDiMPA32076, a nucleic acid molecule that includes at least a portion of adult nDiMPA32032, a nucleic acid molecule that includes at least a portion of adult nDiMPA32028, or a nucleic acid molecule that includes at least a portion of nDiCP143. Particularly preferred nucleic acid molecules to include in recombinant vectors of the present invention include nDiMPA1689, nDiMPA11299, nDiMPA22126, nDiMPA2804, nDiMPA2271, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, adult nDiMPA32028, BvMPA2 nDiCP143 and nDiCP142.
Isolated proteins of the present invention can be produced in a variety of ways, including production and recovery of natural proteins, production and recovery of recombinant proteins, and chemical synthesis of the proteins. In one embodiment, an isolated protein of the present invention is produced by culturing a cell capable of expressing the protein under conditions effective to produce the protein, and recovering the protein. A preferred cell to culture is a recombinant cell that is capable of expressing the protein, the recombinant cell being produced by transforming a host cell with one or more nucleic acid molecules of the present invention. Transformation of a nucleic acid molecule into a cell can be accomplished by any method by which a nucleic acid molecule can be inserted into the cell. Transformation techniques include, but are not limited to, transfection, electroporation, microinjection, lipofection, adsorption, and protoplast fusion. A recombinant cell may remain unicellular or may grow into a tissue, organ or a multicellular organism. Transformed nucleic acid molecules of the present invention can remain extrachromosomal or can integrate into one or more sites within a chromosome of the transformed (i.e., recombinant) cell in such a manner that their ability to be expressed is retained. A preferred nucleic acid molecule with which to transform a cell is a nucleic acid molecule that includes a parasite astacin metalloendopeptidase nucleic acid molecule and/or a filariid cysteine protease nucleic acid molecule of the present invention. Particularly preferred nucleic acid molecules with which to transform cells include nDiMPA1689 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:20), nDiMPA11299 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:l), nDiMPA22126 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:2), nDiMPA2804 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:21), nDiMPA2271 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:22), L3 nDiMPA32292 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:29), L3 nDiMPA2076 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:30), adult nDiMPA32032 (characterized by a coding strand having the nucleic acid sequence SEQ ID NO:32), adult nDiMPA32028 (characterized by a coding strand having the nucleic acid sequence SEQ ID NO:33), BvMPA2, nDiCP143 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:12) and nDiCP142 (characterized by a coding strand having the nucleic acid sequence of SEQ ID NO:23).
Suitable host cells to transform include any cell that can be transformed. Host cells can be either untransformed cells or cells that are already transformed with at least one nucleic acid molecule. Host cells of the present invention either can be endogenously (i.e., naturally) capable of producing parasite, including D. immitis, proteins of the present invention or can be capable of producing such proteins after being transformed with at least one nucleic acid molecule of the present invention. Host cells of the present invention can be any cell capable of producing at least one protein of the present invention, including bacterial, fungal (including yeast), animal parasite (including helminth, protozoa and ectoparasite), insect, animal and plant cells. Preferred host cells include bacterial, mycobacterial, yeast, helminth, insect and mammalian cells. More preferred host cells include Salmonella, Escherichia, Bacillus, Saccharomyces, Spodoptera, Mycobacteria, Trichoplusia, BHK (baby hamster kidney) cells, MDCK cells (normal dog kidney cell line for canine herpesvirus cultivation), CRFK cells (normal cat kidney cell line for feline herpesvirus cultivation) and COS cells. Particularly preferred host cells are Escherichia coli, including E. coli K-12 derivatives; Salmonella typhi; Salmonella typhimurium, including attenuated strains such as UK-1 X3987 and SR-11 40X72; Spodoptera frugiperda; Trichoplusia ni; BHK cells; MDCK cells; CRFK cells and non-tumorigenic mouse myoblast G8 cells (e.g., ATCC CRL 1246). Additional appropriate mammalian cell hosts include other kidney cell lines (e.g., CV-1 monkey kidney cell lines), other fibroblast cell lines (e.g., human, murine or chicken embryo fibroblast cell lines), myeloma cell lines, Chinese hamster ovary cells and/or HeLa cells.
A recombinant cell is preferably produced by transforming a host cell with one or more recombinant molecules, each comprising one or more nucleic acid molecules of the present invention operatively linked to an expression vector containing one or more transcription control sequences. The phrase operatively linked refers to insertion of a nucleic acid molecule into an expression vector in a manner such that the molecule is able to be expressed when transformed into a host cell. As used herein, an expression vector is a DNA or RNA vector that is capable of transforming a host cell and of effecting expression of a specified nucleic acid molecule. Preferably, the expression vector is also capable of replicating within the host cell. Expression vectors can be either prokaryotic or eukaryotic, and are typically viruses or plasmids. Expression vectors of the present invention include any vectors that function (i.e., direct gene expression) in recombinant cells of the present invention, including in bacterial, fungal, animal parasite, insect, animal, and plant cells. Preferred expression vectors of the present invention can direct gene expression in bacterial, yeast, helminth or other parasite, insect and mammalian cells and more preferably in the cell types heretofore disclosed.
Expression vectors of the present invention may also (a) contain secretory signals (i.e., signal segment nucleic acid sequences) to enable an expressed protein of the present invention (i.e., a parasite astacin metalloendopeptidase protein and/or a filariid cysteine protease protein) to be secreted from the cell that produces the protein and/or (b) contain fusion sequences which lead to the expression of inserted nucleic acid molecules of the present invention as fusion proteins. Eukaryotic recombinant molecules may include intervening and/or untranslated sequences surrounding and/or within the nucleic acid sequences of nucleic acid molecules of the present invention. Examples of suitable fusion segments encoded by fusion segment nucleic acids have been disclosed. Suitable signal segments include natural signal segments (e.g., a parasite astacin metalloendopeptidase or cysteine protease signal segment) or any heterologous signal segment capable of directing the secretion of a protein of the present invention. Preferred signal segments include, but are not limited to, tissue plasminogen activator (t-PA), interferon, interleukin, growth hormone, histocompatibility and viral envelope glycoprotein signal segments.
Nucleic acid molecules of the present invention can be operatively linked to expression vectors containing regulatory sequences such as promoters, operators, repressors, enhancers, termination sequences, origins of replication, and other regulatory sequences that are compatible with the recombinant cell and that control the expression of nucleic acid molecules of the present invention. In particular, recombinant molecules of the present invention include transcription control sequences. Transcription control sequences are sequences which control the initiation, elongation, and termination of transcription. Particularly important transcription control sequences are those which control transcription initiation, such as promoter, enhancer, operator and repressor sequences. Suitable transcription control sequences include any transcription control sequence that can function in at least one of the recombinant cells of the present invention. A variety of such transcription control sequences are known to those skilled in the art. Preferred transcription control sequences include those which function in bacterial, yeast, helminth or other parasite, insect and mammalian cells, such as, but not limited to, tac, lac, trp, trc, oxy-pro, omp/lpp, rrnB, bacteriophage lambda (X) (such as xcexpL and xcexpR and fusions that include such promoters), bacteriophage T7, T71ac, bacteriophage T3, bacteriophage SP6, bacteriophage SP01, metallothionein, alpha mating factor, Pichia alcohol oxidase, alphavirus subgenomic promoters (such as Sindbis virus subgenomic promoters), baculovirus, Heliothis zea insect virus, vaccinia virus, herpesvirus, poxyirus, adenovirus, simian virus 40, retrovirus actin, retroviral long terminal repeat, Rous sarcoma virus, heat shock, phosphate and nitrate transcription control sequences as well as other sequences capable of controlling gene expression in prokaryotic or eukaryotic cells. Additional suitable transcription control sequences include tissue-specific promoters and enhancers as well as lymphokine-inducible promoters (e.g., promoters inducible by interferons or interleukins). Transcription control sequences of the present invention can also include naturally occurring transcription control sequences naturally associated with a parasitic helminth, such as a D. immitis, molecule prior to isolation.
A recombinant molecule of the present invention is a molecule that can include at least one of any nucleic acid molecule heretofore described operatively linked to at least one of any transcription control sequence capable of effectively regulating expression of the nucleic acid molecule(s) in the cell to be transformed, examples of which are disclosed herein. Particularly preferred recombinant molecules include pxcex2gal-nDiMPA11299, pxcex2gal-nDiMPA22126, ptrcHis-nDiMPA2804, pxcexPRHis-nDiMPA2804, pBBIII-nDiMPA22126, pxcex2gal-L3-nDiMPA32292, pxcex2gal-L3-nDiMPA32076, pxcex2gal-adult-nDiMPA32032, pxcex2gal-adult-nDiMPA32028 and ptrcHis-nDICP142. Details regarding the production of such recombinant molecules is disclosed herein.
A recombinant cell of the present invention includes any cell transformed with at least one of any nucleic acid molecule of the present invention. A preferred recombinant cell is a cell transformed with a nucleic acid molecule that includes at least a portion of a parasite astacin metalloendopeptidase nucleic acid molecule, such as nDiMPA1689, nDiMPA11299, nDiMPA22126, nDiMPA2804, nDiMPA2271, L3 nDiMPA32292, L3 nDiMPA32076, adult nDiMPA32032, adult nDiMPA32028, or BvMPA2 and/or at least a portion of a filariid cysteine protease nucleic acid molecule, such as a nucleic acid molecule including nDiCP143 or nDiCP142. Particularly preferred recombinant cells include E. coli:pxcex2gal-nDiMPA11299, E. coli:pxcex2gal-nDiMPA22126, E. coli:ptrcHis-nDiMPA2804, E. coli:pxcexPRHis-nDiMPA2804, S. frugiperda:pBBIII-nDiMPA22126, E. coli:pxcex2gal-L3-nDiMPA32292, E. coli:pxcex2gal-L3-nDiMPA32076, E. coli:pxcex2gal-adult-nDiMPA32032, E. coli:pxcex2gal-adult-nDiMPA32028, and E. coli:ptrcHis-nDiCP142. Details regarding the production of these recombinant cells is disclosed herein.
Recombinant cells of the present invention can also be co-transformed with one or more recombinant molecules including nucleic acid molecules encoding one or more proteins of the present invention (e.g., parasite astacin metalloendopeptidase proteins and/or filariid cysteine protease proteins) and one or more other proteins useful in the production of multivalent vaccines which can include one or more protective compounds.
It may be appreciated by one skilled in the art that use of recombinant DNA technologies can improve expression of transformed nucleic acid molecules by manipulating, for example, the number of copies of the nucleic acid molecules within a host cell, the efficiency with which those nucleic acid molecules are transcribed, the efficiency with which the resultant transcripts are translated, and the efficiency of post-translational modifications. Recombinant techniques useful for increasing the expression of nucleic acid molecules of the present invention include, but are not limited to, operatively linking nucleic acid molecules to high-copy number plasmids, integration of the nucleic acid molecules into one or more host cell chromosomes, addition of vector stability sequences to plasmids, substitutions or modifications of transcription control signals (e.g., promoters, operators, enhancers), substitutions or modifications of translational control signals (e.g., ribosome binding sites, Shine-Dalgarno sequences), modification of nucleic acid molecules of the present invention to correspond to the codon usage of the host cell, deletion of sequences that destabilize transcripts, and use of control signals that temporally separate recombinant cell growth from recombinant enzyme production during fermentation. The activity of an expressed recombinant protein of the present invention may be improved by fragmenting, modifying, or derivatizing nucleic acid molecules encoding such a protein.
In accordance with the present invention, recombinant cells of the present invention can be used to produce one or more proteins of the present invention by culturing such cells under conditions effective to produce such a protein, and recovering the protein. Effective conditions to produce a protein include, but are not limited to, appropriate media, bioreactor, temperature, pH and oxygen conditions that permit protein production. An appropriate medium refers to any medium in which a cell of the present invention, when cultured, is capable of producing a parasite protein, including a D. immitis protein, of the present invention. An effective medium is typically an aqueous medium comprising assimilable carbohydrate, nitrogen and phosphate sources, as well as appropriate salts, minerals, metals and other nutrients, such as vitamins. The medium may comprise complex nutrients or may be a defined minimal medium. Cells of the present invention can be cultured in conventional fermentation bioreactors, which include, but are not limited to, batch, fed-batch, cell recycle, and continuous fermentors. Culturing can also be conducted in shake flasks, test tubes, microtiter dishes, and petri plates. Culturing is carried out at a temperature, pH and oxygen content appropriate for the recombinant cell. Such culturing conditions are well within the expertise of one of ordinary skill in the art. Examples of suitable conditions are included in the Examples section.
Depending on the vector and host system used for production, resultant proteins of the present invention may either remain within the recombinant cell; be secreted into the fermentation medium; be secreted into a space between two cellular membranes, such as the periplasmic space in E. coli; or be retained on the outer surface of a cell or viral membrane. The phrase xe2x80x9crecovering the proteinxe2x80x9d refers simply to collecting the whole fermentation medium containing the protein and need not imply additional steps of separation or purification. Proteins of the present invention can be purified using a variety of standard protein purification techniques, such as, but not limited to, affinity chromatography, ion exchange chromatography, filtration, electrophoresis, hydrophobic interaction chromatography, gel filtration chromatography, reverse phase chromatography, concanavalin A chromatography, chromatofocusing and differential solubilization. Proteins of the present invention are preferably retrieved in xe2x80x9csubstantially purexe2x80x9d form. As used herein, xe2x80x9csubstantially purexe2x80x9d refers to a purity that allows for the effective use of the protein as a therapeutic composition or diagnostic. A vaccine for animals, for example, should exhibit no substantial toxicity and should be capable of stimulating the production of antibodies in a vaccinated animal.
The present invention also includes isolated antibodies capable of selectively binding to a protein of the present invention or to a mimetope thereof. Antibodies capable of selectively binding to a parasite astacin metalloendopeptidase protein of the present invention are referred to as anti-parasite astacin metalloendopeptidase antibodies. A particularly preferred antibody of this embodiment is an anti-D. immitis astacin metalloendopeptidase antibody. Antibodies capable of selectively binding to a filariid cysteine protease protein of the present invention are referred to as anti-filariid cysteine protease antibodies. A particularly preferred antibody of this embodiment is an anti-D. immitis cysteine protease antibody. Isolated antibodies are antibodies that have been removed from their natural milieu. The term xe2x80x9cisolatedxe2x80x9d does not refer to the state of purity of such antibodies. As such, isolated antibodies can include anti-sera containing such antibodies, or antibodies that have been purified to varying degrees. As used herein, the term xe2x80x9cselectively binds toxe2x80x9d refers to the ability of such antibodies to preferentially bind to specified proteins and mimetopes thereof of the present invention. Binding can be measured using a variety of methods known to those skilled in the art including immunoblot assays, immunoprecipitation assays, radioimmunoassays, enzyme immunoassays (e.g., ELISA), immunofluorescent antibody assays and immunoelectron microscopy; see, for example, Sambrook et al., ibid.
Antibodies of the present invention can be either polyclonal or monoclonal antibodies. Antibodies of the present invention include functional equivalents such as antibody fragments and genetically-engineered antibodies, including single chain antibodies, that are capable of selectively binding to at least one of the epitopes of the protein or mimetope used to obtain the antibodies. Preferred antibodies are raised in response to proteins, or mimetopes thereof, that are encoded, at least in part, by a nucleic acid molecule of the present invention.
A preferred method to produce antibodies of the present invention includes (a) administering to an animal an effective amount of a protein or mimetope thereof of the present invention to produce the antibodies and (b) recovering the antibodies. Antibodies raised against defined proteins or mimetopes can be advantageous because such antibodies are not substantially contaminated with antibodies against other substances that might otherwise cause interference in a diagnostic assay or side effects if used in a therapeutic composition.
Antibodies of the present invention have a variety of potential uses that are within the scope of the present invention. For example, such antibodies can be used (a) as vaccines to passively immunize an animal in order to protect the animal from parasites susceptible to treatment by such antibodies, (b) as reagents in assays to detect infection by such parasites and/or (c) as tools to recover desired proteins of the present invention from a mixture of proteins and other contaminants.
Furthermore, antibodies of the present invention can be used to target cytotoxic agents to parasites of the present invention in order to directly kill such parasites. Targeting can be accomplished by conjugating (i.e., stably joining) such antibodies to the cytotoxic agents using techniques known to those skilled in the art. Suitable cytotoxic agents include, but are not limited to: double-chain toxins (i.e., toxins having A and B chains), such as diphtheria toxin, ricin toxin, Pseudomonas exotoxin, modeccin toxin, abrin toxin, and shiga toxin; single-chain toxins, such as pokeweed antiviral protein, a-amanitin, and ribosome inhibiting proteins; and chemical toxins, such as melphalan, methotrexate, nitrogen mustard, doxorubicin and daunomycin. Preferred double-chain toxins are modified to include the toxic domain and translocation domain of the toxin but lack the toxin""s intrinsic cell binding domain.
One embodiment of the present invention is a therapeutic composition that, when administered to an animal in an effective manner, is capable of protecting that animal from disease caused by a parasite that is susceptible to at least one of the following treatments: immunization with an isolated parasite astacin metalloendopeptidase of the present invention, immunization with an isolated filariid cysteine protease of the present invention, administration of an inhibitor of astacin metalloendopeptidase activity or administration of an inhibitor of cysteine protease activity. As used herein, a parasite that is susceptible to such a treatment is a parasite that, if such treatment is administered to an animal in an effective manner, shows substantially reduced ability to cause disease in the animal. It is to be understood that such parasite can be susceptible to treatments other than just those listed immediately above. Such treatments can include, but are not limited to, additional treatments, or therapeutic compositions, disclosed herein.
Therapeutic compositions of the present invention include at least one of the following protective compounds: (a) an isolated parasite astacin metalloendopeptidase protein or a mimetope thereof; (b) an isolated parasite nucleic acid molecule capable of hybridizing under stringent conditions with a D. immitis astacin metalloendopeptidase gene; (c) an anti-parasite astacin metalloendopeptidase antibody; (d) an inhibitor of astacin metalloendopeptidase activity identified by its ability to inhibit parasite astacin metalloendopeptidase activity; (e) an isolated filariid nematode cysteine protease protein or a mimetope thereof; (f) an isolated filariid nematode nucleic acid molecule capable of hybridizing under stringent conditions with a D. immitis cysteine protease gene; (g) an anti-filariid nematode cysteine protease antibody; and (h) an inhibitor of cysteine protease activity identified by its ability to inhibit filariid nematode cysteine protease activity. As used herein, a protective compound refers to a compound that, when administered to an animal in an effective manner, is able to treat, ameliorate, and/or prevent disease caused by a parasite of the present invention. Preferred parasites to target are heretofore disclosed. Examples of proteins, nucleic acid molecules and antibodies of the present invention are disclosed herein. Astacin metalloendopeptidase inhibitors and cysteine protease inhibitors of the present invention are described in more detail below.
The present invention also includes a therapeutic composition comprising at least one astacin parasite metalloendopeptidase-based or filariid nematode cysteine protease-based protective compound of the present invention in combination with at least one additional compound protective against one or more infectious agents. Examples of such compounds and infectious agents are heretofore disclosed.
Therapeutic compositions of the present invention can be administered to any animal susceptible to such therapy, preferably to mammals, and more preferably to dogs, cats, humans, ferrets, horses, cattle, sheep and other pets and/or economic food animals. Preferred animals to protect include dogs, cats, humans and ferrets, with dogs and cats being particularly preferred.
In one embodiment, a therapeutic composition of the present invention can be administered to the vector in which the parasite develops from a microfilaria into L3, such as to a mosquito in order to prevent the spread of heartworm. Such administration could be orally or by developing transgenic vectors capable of producing at least one therapeutic composition of the present invention. In another embodiment, a vector, such as a mosquito, can ingest therapeutic compositions present in the blood of a host that has been administered a therapeutic composition of the present invention.
Therapeutic compositions of the present invention can be formulated in an excipient that the animal to be treated can tolerate. Examples of such excipients include water, saline, Ringer""s solution, dextrose solution, Hank""s solution, and other aqueous physiologically balanced salt solutions. Nonaqueous vehicles, such as fixed oils, sesame oil, ethyl oleate, or triglycerides may also be used. Other useful formulations include suspensions containing viscosity enhancing agents, such as sodium carboxymethylcellulose, sorbitol, or dextran. Excipients can also contain minor amounts of additives, such as substances that enhance isotonicity and chemical stability. Examples of buffers include phosphate buffer, bicarbonate buffer and Tris buffer, while examples of preservatives include thimerosal, m- or o-cresol, formalin and benzyl alcohol. Standard formulations can either be liquid injectables or solids which can be taken up in a suitable liquid as a suspension or solution for injection. Thus, in a non-liquid formulation, the excipient can comprise dextrose, human serum albumin, preservatives, etc., to which sterile water or saline can be added prior to administration.
In one embodiment of the present invention, the therapeutic composition can also include an immunopotentiator, such as an adjuvant or a carrier. Adjuvants are typically substances that generally enhance the immune response of an animal to a specific antigen. Suitable adjuvants include, but are not limited to, Freund""s adjuvant; other bacterial cell wall components; aluminum-based salts; calcium-based salts; silica; polynucleotides; toxoids; serum proteins; viral coat proteins; other bacterial-derived preparations; gamma interferon; block copolymer adjuvants, such as Hunter""s Titermax adjuvant (Vaxcel(trademark), Inc. Norcross, Ga.); Ribi adjuvants (available from Ribi ImmunoChem Research, Inc., Hamilton, Mont.); and saponins and their derivatives, such as Quil A (available from Superfos Biosector A/S, Denmark). Carriers are typically compounds that increase the half-life of a therapeutic composition in the treated animal. Suitable carriers include, but are not limited to, polymeric controlled release formulations, biodegradable implants, liposomes, bacteria, viruses, oils, esters, and glycols.
In order to protect an animal from disease caused by a parasite of the present invention, a therapeutic composition of the present invention is administered to the animal in an effective manner such that the composition is capable of protecting that animal from a disease caused by a parasite. For example, an isolated protein or mimetope thereof, when administered to an animal in an effective manner, is able to elicit (i.e., stimulate) an immune response, preferably including both a humoral and cellular response, that is sufficient to protect the animal from the disease. Similarly, an antibody of the present invention, when administered to an animal in an effective manner, is administered in an amount so as to be present in the animal at a titer that is sufficient to protect the animal from the disease, at least temporarily. Oligonucleotide nucleic acid molecules of the present invention can also be administered in an effective manner, thereby reducing expression of astacin metalloendopeptidase or cysteine protease proteins in order to interfere with development of parasites targeted in accordance with the present invention.
Therapeutic compositions of the present invention can be administered to animals prior to infection in order to prevent infection and/or can be administered to animals after infection in order to treat disease caused by the parasite. For example, proteins, mimetopes thereof, and antibodies thereof can be used as immunotherapeutic agents. Acceptable protocols to administer therapeutic compositions in an effective manner include individual dose size, number of doses, frequency of dose administration, and mode of administration. Determination of such protocols can be accomplished by those skilled in the art. A suitable single dose is a dose that is capable of protecting an animal from disease when administered one or more times over a suitable time period. For example, a preferred single dose of a protein, mimetope or antibody therapeutic composition is from about 1 microgram (xcexcg) to about 10 milligrams (mg) of the therapeutic composition per kilogram body weight of the animal. Booster vaccinations can be administered from about 2 weeks to several years after the original administration. Booster vaccinations preferably are administered when the immune response of the animal becomes insufficient to protect the animal from disease. A preferred administration schedule is one in which from about 10 xcexcg to about 1 mg of the vaccine per kg body weight of the animal is administered from about one to about two times over a time period of from about 2 weeks to about 12 months. Modes of administration can include, but are not limited to, subcutaneous, intradermal, intravenous, nasal, oral, transdermal and intramuscular routes.
According to one embodiment, a nucleic acid molecule of the present invention can be administered to an animal in a fashion to enable expression of that nucleic acid molecule into a protective protein or protective RNA (e.g., antisense RNA, ribozyme or RNA drug) in the animal to be protected from disease. Nucleic acid molecules can be delivered to an animal in a variety of methods including, but not limited to, (a)direct injection (e.g., as xe2x80x9cnakedxe2x80x9d DNA or RNA molecules, such as is taught, for example in Wolff et al., 1990, Science 247, 1465-1468) or (b) packaged as a recombinant virus particle vaccine or as a recombinant cell vaccine (i.e., delivered to a cell by a vehicle selected from the group consisting of a recombinant virus particle vaccine and a recombinant cell vaccine)
A recombinant virus particle vaccine of the present invention includes a recombinant molecule of the present invention that is packaged in a viral coat and that can be expressed in an animal after administration. Preferably, the recombinant molecule is packaging-deficient. A number of recombinant virus particles can be used, including, but not limited to, those based on alphaviruses, poxyiruses, adenoviruses, herpesviruses, and retroviruses. Preferred recombinant particle viruses are those based on alphaviruses (such as Sindbis virus), herpesviruses and poxyiruses. Methods to produce and use recombinant virus particle vaccines are disclosed in U.S. patent application Ser. No. 08/015/414, filed Feb. 8, 1993, entitled xe2x80x9cRecombinant Virus Particle Vaccinesxe2x80x9d, which is incorporated by reference herein in its entirety.
When administered to an animal, a recombinant virus particle vaccine of the present invention infects cells within the immunized animal and directs the production of a protective protein or RNA nucleic acid molecule that is capable of protecting the animal from disease caused by a parasite of the present invention. For example, a recombinant virus particle comprising a D. immitis astacin metalloendopeptidase nucleic acid molecule and/or a D. immitis cysteine protease nucleic acid molecule of the present invention is administered according to a protocol that results in the animal producing a sufficient immune response to protect itself from heartworm. A preferred single dose of a recombinant virus particle vaccine of the present invention is from about 1xc3x97104 to about 1xc3x97107 virus plaque forming units (pfu) per kilogram body weight of the animal. Administration protocols are similar to those described herein for protein-based vaccines.
A recombinant cell vaccine of the present invention includes recombinant cells of the present invention that express at least one protein of the present invention. Preferred recombinant cells include Salmonella, E. coli, Mycobacterium, S. frugiperda, baby hamster kidney, myoblast G8, COS, MDCK and CRFK recombinant cells, with Salmonella recombinant cells being more preferred. Such recombinant cells can be administered in a variety of ways but have the advantage that they can be administered orally, preferably at doses ranging from about 108 to about 1012 bacteria per kilogram body weight. Administration protocols are similar to those described herein for protein-based vaccines. Recombinant cell vaccines can comprise whole cells or cell lysates.
In common with most other enteric pathogens, Salmonella strains normally enter the host orally. Once in the intestine, they interact with the mucosal surface, normally to establish an invasive infection. Most Salmonella infections are controlled at the epithelial surface, causing the typical Salmonella-induced gastroenteritis. Some strains of Salmonella, including S. typhi and some S. typhimurium isolates, have evolved the ability to penetrate deeper into the host, causing a disseminated systemic infection. It appears such strains have the capacity to resist the killing actions of macrophages and other immune cells. S. typhi can exist for long periods as a facultative intracellular parasite. Some of the live vaccine strains can also persist for long periods in the mononuclear phagocyte system. Hosts infected in such a manner develop, in addition to a mucosal immune response, systemic cellular and serum antibody responses to the Salmonella. Thus, invading Salmonella, whether virulent or attenuated, can stimulate strong immune responses, unlike many other enteric pathogens which only set up local, noninvasive gut infections. The potent immunogenicity of live Salmonella makes them attractive candidates for carrying nucleic acid molecules of the present invention, and the proteins they encode, to the immune system.
A preferred recombinant cell-based vaccine is one in which the cell is attenuated. Salmonella typhimurium strains, for example, can be attenuated by introducing mutations into genes critical for in vivo growth and survival. For example, genes encoding cyclic adenosine monophosphate (cAMP) receptor protein or adenylate cyclase are deleted to produce avirulent, vaccine strains. Such strains can deliver antigens to lymphoid tissue in the gut but demonstrate reduced capacity to invade the spleen and mesenteric lymph nodes. These strains are still capable of stimulating both humoral and cellular immunity in mammalian hosts.
Recombinant cell vaccines can be used to introduce proteins of the present invention into the immune systems of animals. For example, recombinant molecules comprising nucleic acid molecules of the present invention operatively linked to expression vectors that function in Salmonella can be transformed into Salmonella host cells. The resultant recombinant cells are then introduced into the animal to be protected. Preferred Salmonella host cells are those for which survival depends on their ability to maintain the recombinant molecule (i.e., a balanced-lethal host-vector system). An example of such a preferred host recombinant molecule combination is a Salmonella strain (e.g., UK-1 X3987 or SR-11 X4072) which is unable to produce aspartate xcex2-semialdehyde dehydrogenase in combination with a recombinant molecule also capable of encoding the enzyme. Aspartate xcex2-semialdehyde dehydrogenase, encoded by the asd gene, is an important enzyme in the pathway to produce diaminopimelic acid (DAP). DAP is an essential component of the peptidoglycan of the cell wall of Gram-negative bacteria, such as Salmonella, and, as such, is necessary for survival of the cell. Thus, Salmonella lacking a functional asd gene can only survive if they maintain a recombinant molecule that is also capable of expressing a functional asd gene.
In one embodiment, a nucleic acid molecule of the present invention is inserted into expression vector pTECH-1 (available from Medeva, London, U.K.) and the resulting recombinant molecule is transfected into a Salmonella strain, such as BRD 509 (available from Medeva), to form a recombinant cell. Such recombinant cells can be used to produce the corresponding encoded protein or can be used as recombinant cell vaccines.
One preferred embodiment of the present invention is the use of nucleic acid molecules and proteins of the present invention, and particularly D. immitis nucleic acid molecules and proteins of the present invention, to protect an animal from heartworm. Preferred therapeutic compositions are those that are able to inhibit at least one step in the portion of the parasite""s development cycle that includes L3 larvae, third molt, L4 larvae, fourth molt and immature adult prior to entering the circulatory system. In dogs, this portion of the development cycle is about 70 days. As such, preferred therapeutic compositions include D. immitis astacin metalloendopeptidase-based and D. immitis cysteine protease-based therapeutic compounds of the present invention. Such compositions are administered to animals in a manner effective to protect the animals from heartworm. Additional protection may be obtained by administering additional protective compounds, including other D. immitis proteins, nucleic acid molecules and antibodies as heretofore disclosed.
One embodiment of the present invention is the use of enzymatically active parasite astacin metalloendopeptidase and/or filariid nematode cysteine protease proteins of the present invention to identify inhibitors of such enzyme activity. While not being bound by theory, it is believed that parasites use such proteases in a number of ways, including, but not limited to, to effect embryonic and larval development, to effect molting and to effect tissue migration both as larvae and adults. Such proteases are capable of degrading cutaneous connective tissue macromolecules as well as other proteinaceous material to facilitate such functions. It is also of interest that astacin metalloendopeptidases identified in sea urchins, Drosophila and Xenopus have been linked with development and maturation of the respectively organisms. As such, inhibitors of astacin metalloendopeptidase and/or cysteine protease activity could be particularly beneficial in disrupting embryonic and/or larval development or molting by parasites in general and tissue migration by those parasites capable of such migration. Use of parasite enzymes to develop such inhibitors is also advantageous because inhibitors can be identified that are highly selective for the parasite without causing undue side effects to the animal being treated.
One therapeutic composition of the present invention includes an inhibitor of parasite astacin metalloendopeptidase activity, i.e., a compound capable of substantially interfering with the function of a parasite astacin metalloendopeptidase susceptible to inhibition by an inhibitor of D. immitis astacin metalloendopeptidase activity. An inhibitor of astacin metalloendopeptidase can be identified using enzymatically active parasite and preferably D. immitis, astacin metalloendopeptidase proteins of the present invention.
One embodiment of the present invention is a method to identify a compound capable of inhibiting astacin metalloendopeptidase activity of a parasite. Such a method includes the steps of (a) contacting (e.g., combining, mixing) an isolated parasite, preferably D. immitis, astacin metalloendopeptidase protein with a putative inhibitory compound under conditions in which, in the absence of the compound, the protein has astacin metalloendopeptidase activity, and (b) determining if the putative inhibitory compound inhibits the astacin metalloendopeptidase activity. Putative inhibitory compounds to screen include organic molecules, antibodies (including functional equivalents thereof) and substrate analogs. Methods to determine astacin metalloendopeptidase activity are known to those skilled in the art; see, for example, Gomis-Ruth, et al. ibid., and referenced cited therein.
The present invention also includes a test kit to identify a compound capable of inhibiting astacin metalloendopeptidase activity of a parasite. Such a test kit includes an isolated parasite, preferably D. immitis, astacin metalloendopeptidase protein having astacin metalloendopeptidase activity and a means for determining the extent of inhibition of astacin metalloendopeptidase activity in the presence of (i.e., effected by) a putative inhibitory compound.
Astacin metalloendopeptidase inhibitors isolated by such a method, and/or test kit, can be used to inhibit any astacin metalloendopeptidase that is susceptible to such an inhibitor. Preferred astacin metalloendopeptidase enzymes to inhibit are those produced by parasites. A particularly preferred as acin metalloendopeptidase inhibitor of the present invention is capable of protecting an animal from heartworm. It is also within the scope of the present invention to use inhibitors of the present invention to target astacin metalloendopeptidase-related disorders in animals. Therapeutic compositions comprising astacin metalloendopeptidase inhibitory compounds of the present invention can be administered to animals in an effective manner to protect animals from disease caused by the targeted astacin metalloendopeptidase enzymes, and preferably to protect animals from heartworm. Effective amounts and dosing regimens can be determined using techniques known to those skilled in the art.
Another therapeutic composition of the present invention includes an inhibitor of parasite cysteine protease activity, i.e., a compound capable of substantially interfering with the function of a parasite cysteine protease susceptible to inhibition by an inhibitor of filariid nematode cysteine protease activity. A cysteine protease inhibitor can be identified using enzymatically active filariid nematode, and preferably D. immitis, cysteine protease proteins of the present invention.
One embodiment of the present invention is a method to identify a compound capable of inhibiting cysteine protease activity of a parasite. Such a method includes the steps of (a) contacting (e.g., combining, mixing) an isolated filariid nematode, preferably D. immitis, cysteine protease protein with a putative inhibitory compound under conditions in which, in the absence of the compound, the protein has cysteine protease activity, and (b) determining if the putative inhibitory compound inhibits the cysteine protease activity. Putative inhibitory compounds to screen include organic molecules, antibodies (including functional equivalents thereof) and substrate analogs. Methods to determine cysteine protease activity are known to those skilled in the art, as heretofore disclosed.
The present invention also includes a test kit to identify a compound capable of inhibiting cysteine protease activity of a parasite. Such a test kit includes an isolated filariid nematode, preferably D. immitis, cysteine protease protein having cysteine protease activity and a means for determining the extent of inhibition of cysteine protease activity in the presence of (i.e., effected by) a putative inhibitory compound.
Inhibitors isolated by such a method, and/or test kit, can be used to inhibit any cysteine protease that is susceptible to such an inhibitor. Preferred cysteine protease enzymes to inhibit are those produced by parasites. A particularly preferred cysteine protease inhibitor of the present invention is capable of protecting an animal from heartworm. It is also within the scope of the present invention to use inhibitors of the present invention to target cysteine protease-related disorders in animals. Therapeutic compositions comprising cysteine protease-inhibitory compounds of the present invention can be administered to animals in an effective manner to protect animals from disease caused by the targeted cysteine protease. Effective amounts and dosing regimens can be determined using techniques known to those skilled in the art.
The efficacy of a therapeutic composition of the present invention to protect an animal from disease caused by a parasite can be tested in a variety of ways including, but not limited to, detection of protective antibodies (using, for example, proteins or mimetopes of the present invention), detection of cellular immunity within the treated animal, or challenge of the treated animal with the parasite to determine whether the treated animal is resistant to disease. Such techniques are known to those skilled in the art.
In accordance with the present invention, the inventors have shown that protease inhibitors can inhibit parasite larval development. For example, bestatin and phosphoramidon have been shown to inhibit molting of D. immitis larvae, as described in more detail in the Examples.
Another embodiment of the present invention includes the isolation of proteases, including metalloproteases and cysteine proteases from parasitic larval excretory/secretory (ES) products. Using a modified version of the protocol first described in U.S. patent application Ser. No. 08/153,554, ibid., the inventors have, for example, isolated a fraction comprising a protein of approximately 60 kD (as determined by Tris-glycine sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) that has metalloprotease activity as determined by the protein""s ability to cleave H-Phe-AMC. When submitted to size-exclusion chromatography, the active fraction elutes with bovine serum albumin, indicating an approximate molecular weight of from about 62 to about 66 kD. The modified protocol, which is described in more detail in the Examples, includes submitting parasitic, preferably D. immitis, larval ES, to anion exchange chromatography, followed by size exclusion chromatography and isoelectric focussing. The active fraction has a pI of about 6.8.
In another embodiment, the inventors have identified at least one parasite metalloprotease from the ES that is capable of degrading collagen. For example, electrophoresis of D. immitis larval ES through a gelatin-based matrix leads to isolated active fractions that migrate with apparent molecular weights of about 60, 95 and at least about 200 kD. The proteolytic activity of such fractions is essentially completely inhibited by EDTA.
It is also within the scope of the present invention to use isolated proteins, mimetopes, nucleic acid molecules and antibodies of the present invention as diagnostic reagents to detect infection by parasites. Such diagnostic reagents can be supplemented with additional compounds that can detect other phases of the parasite""s life cycle.
The following examples are provided for the purposes of illustration and are not intended to limit the scope of the present invention.